Ocular tamponades are vitreous substitutes that are used to reposition the retina of an eye in instances where a reattachment is not achievable by natural healing or by laser coagulation. The purpose of a vitreous substitute is to provide long-term tamponade of the retina, i.e., exhibit an ideal pressure (force/area) to position and maintain the retina in place. Current commercially used tamponades include perfluorocarbon-liquids, balanced salt solutions, silicone oil or fluid and gases, such as air, sulfur hexafluoride (SF6) and perfluorocarbons (PFCs). Silicone oil or fluid is the preferred tamponade in cases of severe retina detachment, where the tamponade is used six months or longer.
Silicone oil or fluid is prepared by a ring-opening polymerization of strained cyclic silicones. The final product consists of relatively high molecular weight silicone fluid and unreacted relatively low molecular weight cyclic siloxanes and oligomers. The unreacted relatively low molecular weight cyclics and oligomers are cytotoxic and have been implicated in an undesirable emulsification phenomenon that sometimes occurs in silicone-based fluids. Accordingly, the unreacted relatively low molecular weight cyclics and oligomers must be removed from the silicone fluid product to be useful as an ocular tamponade. The preferred current method of purifying relatively high molecular weight silicone oil, or silicone fluid, involves the use of a lengthy solvent extraction process whereby the silicone fluid is slowly added to a non-solvent, such as acetone, and allowed to separate. The unreacted low molecular weight cyclics and oligomers are soluble in the non-solvent or acetone phase. The unreacted low molecular weight cyclics and oligomers are thus removed with the non-solvent or acetone phase upon separation thereof from the high molecular weight silicone fluid. Once separated, the non-solvent phase with the low molecular weight cyclics and oligomers becomes an undesirable waste product of the purification method and requires disposal. Likewise, following purification, controls are necessary to ensure the final silicone oil or fluid product is free of non-solvent contamination.
Because of the noted shortcomings of the current, preferred method of silicone fluid purification to remove cytotoxic impurities therefrom, there is a need for a purification method that is effective, less time consuming, eliminates the potential for non-solvent residual contamination and lessens or eliminates non-solvent waste production.